1. Field of the Invention
The present invention relates generally to an optical switch, and more specifically to an optical switch suitable for use in optical communications equipment and optical transmission equipment.
2. Description of the Related Art
With the progress of optical communications, fiber optics communications networks have been increasingly involved with long optical paths and complex branches. Under these circumstances, the need for switching optical paths between circuits has been mounting in optical communications and optical transmission equipment, and an increasing number of optical switches have been used to meet the need.
Various types of optical switches for switching optical paths have so far been proposed, including a type in which the traveling direction of light is switched by electrically altering the refractive index or phase of a light path, and a type in which the traveling direction of light is switched by mechanically moving the light path. Among them, the mechanical optical switch is being widely used in optical communications equipment, optical transmission equipment, etc. because it has low coupling loss, virtually no dependence on the wavelength of propagating light, and such a unique property that even after power is turned off, the light coupling state before turning off the power can be maintained.
Mechanical optical switches include the one disclosed in Japanese Patent No. 3,062,881. This optical switch comprises an electromagnetic actuator (optical switch driver) having a fixed optical fiber holder for holding an output optical fiber end, and a movable optical fiber holder for holding an elastically deformable input optical fiber end, both disposed facing each other via a small gap, so that the movable optical fiber holder is caused to make a relative movement with respect to the fixed optical fiber holder.
Since the mechanical optical switch has a small gap between the input and output optical fibers, the gap is often filled with silicone oil to prevent light from attenuating or scattering in the gap. Silicone oil used for this purpose is called the refractive index matching material. The refractive index matching material is charged into an optical switch housing so that the refractive index matching material fills up a space between the ends of optical fibers. To achieve this, the input optical fiber and the electromagnetic actuator (optical switch driver) must be allowed to move and operate in the refractive index matching material.
The optical switch is usually used not only in temperate regions but also in cold regions, and even outdoors in some cases. In cold regions, there are not a few cases in which temperature falls down to xe2x88x9220xc2x0 C., or even to xe2x88x9250xc2x0 C. in very cold days. Furthermore, even when the optical switch is used indoors, it is often installed in an non-air-conditioned room. It is often exposed to extremely cold temperatures in winter. In such a low temperature, operation of an optical switch having a refractive index matching material might involve some difficulty. This is attributed to that the position of optical fibers in the optical switch is unwantedly shifted, or the viscosity of the refractive index matching material rises, making the optical switch inoperative. When the temperature of the optical switch rises, not only properties of magnetic materials constituting the electromagnetic actuator, the fixed optical fiber holder, and the movable optical fiber holder in the optical switch could deteriorate, but the adhesive resin used to bond the optical switch housing could also deteriorate. This, together with the swelling of the components and the refractive index matching material, could lead to leakage of the refractive index matching material from the bonded parts of the housing.
It is therefore an object of the present invention to provide an optical switch that can ensure proper operation even in low-temperature service environments and prevent the switch from being subjected to excessively high temperatures.
It is another object of the present invention to provide an optical switch that can ensure proper operation with a small optical switch without increasing the thickness thereof.
It is a further object of the present invention to provide an optical switch that in the event of malfunction or failure of proper operation, can keep the switch inoperative until the proper operation of the switch is restored.
The optical switch according to the present invention comprises
a housing,
a fixed optical fiber holder that holds at least one output/input optical fiber end within the housing,
a movable optical fiber holder that holds at least one input/output optical fiber end within the housing, and is allowed to make a relative movement with respect to the fixed optical fiber holder facing it,
a driver for causing the movable optical fiber holder to make a relative movement with respect to the fixed optical fiber holder, and causing at least one input optical fiber end to relatively move from or to a location facing at least one output optical fiber end,
a refractive index matching material packed in the housing and at least between the ends of the output optical fiber and the input optical fiber,
a heater for heating the refractive index matching material within the housing,
a temperature sensing means for detecting the temperature in the housing, and
a controller for turning on and off the power to the heater using the temperature sensing means.
The terms xe2x80x9coutput/input optical fiberxe2x80x9d and xe2x80x9cinput/output optical fiberxe2x80x9d means that when the output optical fiber of the output-input optical fiber is held by the fixed optical fiber holder, the input optical fiber of the input-output optical fiber is held by the movable optical fiber holder, or vice versa. The same holds true throughout the Specification.
In the aforementioned optical switch, the heater and the temperature sensing means should be in contact with the refractive index matching material in the housing. Furthermore, the controller can turn on the power to the heater when the measured value of the temperature sensing means is lower than a first predetermined value, and can turn off the power when the measured value of the temperature sensing means is higher than a second predetermined value. When an instruction to drive the driver is given from outside, the controller can drive the driver in accordance with the measured value of the temperature sensing means. The controller can drive the driver with a delay of a predetermined time after the power to the heater is turned on.
Furthermore, the optical switch according to the present invention can have a second temperature sensing means for detecting the temperature outside the housing. When the measured value of the second temperature sensing means is lower than a predetermined value, the controller can turn on the power to the heater, and when the measured value of the temperature sensing means for detecting the temperature in the housing (internal temperature sensing means) is higher than a second predetermined value, the controller can turn off the power to the heater.
The optical switch according to the present invention can comprise
a housing,
a fixed optical fiber holder that holds at least one output/input optical fiber end within the housing,
a movable optical fiber holder that holds at least one input/output optical fiber end within the housing, and is allowed to make a relative movement with respect to the fixed optical fiber holder facing it,
a driver for causing the movable optical fiber holder to make a relative movement with respect to the fixed optical fiber holder, and causing at least one input optical fiber end to relatively move from or to a location facing at least one output optical fiber end,
a refractive index matching material packed in the housing and at least between the ends of the output optical fiber and the input optical fiber,
a heater for heating the refractive index matching material within the housing, and
a PTC(positive temperature-coefficient) resistive element connected in series to the heater in the housing. The heater and the PTC resistive element should preferably be in contact with the refractive index matching material in the housing. It is also desirable that the PTC resistive element should have its Curie point in the range of 0xc2x0 C. to 60xc2x0 C.
The optical switch according to the present invention can comprise
a housing,
a fixed optical fiber holder that holds at least one output/input optical fiber end within the housing,
a movable optical fiber holder that holds at least one input/output optical fiber end within the housing, and is allowed to make a relative movement with respect to the fixed optical fiber holder facing it,
a driver for causing the movable optical fiber holder to make a relative movement with respect to the fixed optical fiber holder, and causing at least one input optical fiber end to relatively move from or to a location facing at least one output optical fiber end,
a refractive index matching material charged in the housing and at least between the ends of the output optical fiber and the input optical fiber,
a heater for heating the refractive index matching material within the housing, and
a bimetal switch connected in series to the heater in the housing. The heater and the bimetal switch should preferably be in contact with the refractive index matching material in the housing. The bimetal switch can be turned off in the range of 0xc2x0 C. to 60xc2x0 C.
The optical switch according to the present invention can comprise
a housing made of a self-temperature controlled ceramic heater,
a fixed optical fiber holder that holds at least one output/input optical fiber end within the housing,
a movable optical fiber holder that holds at least one input/output optical fiber end within the housing, and is allowed to make a relative movement with respect to the fixed optical fiber holder facing it,
a driver for causing the movable optical fiber holder to make a relative movement with respect to the fixed optical fiber holder, and causing at least one input optical fiber end to relatively move from or to a location facing at least one output optical fiber end,
a refractive index matching material charged in the housing and at least between the ends of the output optical fiber and the input optical fiber, and
current-carrying lead wires connected to the ceramic heater. At least part of the self-temperature controlled ceramic heater should preferably be in contact with the refractive index matching material, and the ceramic heater is a PTC resistive element having a Curie point in the range of 0xc2x0 C. to 60xc2x0 C.